1. Field of the Invention
The present invention relates to a projector for projecting light onto a screen or other projection surface to display an image, and in particular relates to a technique for executing zoom adjustment and keystone correction.
2. Description of the Related Art
When an image is displayed on a projection surface such a screen using a projector, trapezoidal distortion sometime occurs in the image displayed on the projection surface (hereinafter termed “display image”) due to the relative positions of the projector and the projection surface. In such instances, keystone correction is used to correct trapezoidal distortion of the display image.
Keystone correction is carried out by reducing the image to trapezoidal shape and forming the image on the liquid crystal panel of the projector, and thus when there is appreciable trapezoidal distortion of the display image, the image formed on the liquid crystal panel becomes small, resulting in some instances in a drop in image resolution.
In the meanwhile, projectors are equipped with a zoom lens for adjusting the size of the display image on the projection surface. By adjusting the zoom lens (hereinafter referred to as “zoom adjustment”), zoom level can be adjusted between the telephoto end (smaller display image end) and the wide angle end (larger display image end). When a display image is displayed on the projection surface using the projector, it is preferred that a display image is displayed as large as possible on the projection surface.
Various techniques have been disclosed for performing zoom adjustment and keystone correction automatically, while avoiding a drop in resolution. For example, there has been disclosed a technique in JP2000-241874A whereby a test pattern is displayed on the projection surface and captured with a monitor camera, the image so captured being used to carry out zoom adjustment such that the largest possible display image is displayed automatically on the projection surface; and keystone correction is then performed. There has also been disclosed a technique in JP8-292496A whereby a test pattern is displayed on the projection surface, and zoom adjustment is then carried out while determining whether the pattern has reached maximum size within the projection surface.
However, with the prior art mentioned above, since keystone correction is performed after zoom adjustment to display the display image at maximum size on the projection surface, the display image on the projection surface is reduced due to keystone correction, becoming smaller in size. This causes necessity of repeating zoom adjustment.
An additional problem is that conventional zoom adjustment such as that described above is executed repeatedly through process of projecting a test pattern, capturing it with a monitor camera, making a determination, and performing zoom adjustment, until the intended zoom level is determined, making the process very time consuming.